Tone control system



Sept-14, 1937. I K. w. JARVIS 2,093,393

TONE CONTROL SYSTEM Filed Nov. 25, 1950 3 Sheets-Sheet 1 1: GIT-Q. l

, v INVEINITOR; W1 W'- o Y F dog; 8/92 3 Sheets-Sheet 2 Filed Nov. 25, 1930 IIE E Sept. 14,- 1937.

INVENTOR. Jami/a, TIORNEYS] 14, 1937. K. w. JARVIS TONE CONTROL SYSTEM 'Sheef 3 INVENTOR.

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A TTORNEY Patented Sept. 14, 1937 UNETED STATS TENT OFFICE TONE CONTROL SYSTEM Application November 25, 1930, Serial No. 498,150

12 Claims.

My invention relates broadly to audio frequency amplification circuits and more particularly to a tone control system for audio frequency amplification circuits.

One of the objects of my invention is to provide a circuit arrangement for a tone control system in an audio frequency amplification circuit by which correction can be made of the circuit characteristics according to the character of the musi- 10 cal variation or amplitude of the reproduced sound.

Another object of my invention is to provide an interstage coupling circuit arrangement for audio frequency amplifiers by which different porl tions of the coupling circuit may be rendered variably selective to the different frequencies which it is desired to transfer from one electron tube circuit to another for controlling the tone of the reproduced sound. 20 A still further object of my invention is to provide a tone control circuit for coupling the output of one electron tube amplifier stage to the input of a succeeding electron tube amplifier stage including a plurality of impedance branches adapted to be selectively adjusted relative to each other for choosing the degree to which each branch adds for determining the characteristicsof the energy transferred between the amplifier stages for selectively controlling the tone thereof. 30 Other and further objects of my invention reside in the arrangement of frequency selection paths between the stages of an audio frequency amplifier adjustable within predetermined limits for controlling the tone of reproduced sound as more fully set forth in the specification hereinafter following by reference to the accompanying drawings, wherein: V

Figure l diagrammatically illustrates the application of my invention to the circuits of a radio broadcast receiver; Fig. 2 is a diagrammatic view of a tone control circuit embodying my invention; Fig. 3 represents a series of characteristic curves explaining the operation of the tone control circuit of my invention; Fig. 4 shows a modified coupling circuit embodying the tone control system of my invention; Fig. 5 diagrammatically illustrates a further modified circuit embodying the principles of my invention; Fig. 6 illustrates one form of coupling system embodying the principles of my invention including an impedance branch in circuit with one of the coupling transformers for controlling the tone of the energy transferred from one electron tube stage to anr other; Fig. 7 illustrates a tone control circuit of simplified form in which the tone control is incorporated as part of the coupling means between the amplification stages; Fig. 8 illustrates a multiple arrangement of tone control means disposed between the output circuit of one electron tube and the input circuit of a succeeding electron tube; and Fig. 9 shows the application of the tone control circuit of my invention to a three electrode electron tube amplifier system.

While I have shown my invention herein as applied particularly to radio broadcast receivers it is 10 to be understood that the principles of my invention may also be applied to the circuits of electrical phonographs, public address systems, talking motion picture equipment and other sound reproducing apparatus. In radio receivers the problem of tone control is particularly difficult because of the existing background of static and other noises existent in the sound reproducer. No music can seem to be perfectly reproduced with a background of hiss and noise almost as great in amplitude as the signaling energy, resulting in noise practically as loud as the volume of the music. I have found that an effort to eliminate the high audio frequencies tends to improve the noise condition more rapidly than the quality of the music is depreciated with a net increase in enjoyment. However there are many other com siderations which tend to destroy tone effects, among which I may mention fading, phase shifting, lack of true binaural perception and the presence of harmonic frequencies. The failure of the amplifier circuits to follow a substantially flat characteristic introduces undesired differentia tion of note from its normal characteristic. Even though the reproduction may be found faithful at one amplitude, when the amplification is raised it will be found that the tone is changed. In designing the tone control circuit of my invention I have considered the response characteristics of the circuits under varying conditions and for the production of different sensations of hearing and the sense impressions produced thereby. The sense impressions, or quality of a complex sound wave, are due to the apparent loudness of each component frequency. Either a change in loudness or frequency distribution of the sound components will change the sense impression or the apparent quality. This may be due to an actual change in the character of the music, a piano does not sound like a violin. It may be a change due to an increased energy level which produces, as noted above, a radical change in apparent quality. It is this change in quality which has been one of the most elusive factors in reproducing perfect quality. 5

In one tone controlled system of my invention, I provide a multiplicity of energy transfer paths between the stages of the audio frequency amplification system. The passage of energy through the separate paths is regulated by suitable change in effective resistance of the separate paths whereby the energy transfer may be controlled through predetermined paths selected according to the tone characteristics which are to be reproduced. In another form of my invention, the network characteristics of the coupling system determine the response curve rather than the selective predetermined circuits.

Referring to the drawings in more detail, my invention has been shown applied to the audio frequency amplifier system of a radio broadcast receiver which comprises the radio frequency amplifier stages indicated at I, 2, 3 and 4, a detector stage indicated at 5, an audio frequency amplifier indicated at 6, and a push-pull power amplifier system indicated by tubes 1 and 8. Theloud speaker or sound reproducer has been indicated by reference character 30 connected with an output circuit of the power amplifier 'l8. The receiving circuit is indicated as connecting to antenna 9 and ground l through coupling transformer 2| with the input of the radio frequency amplifier system. The radio frequency amplifier stage I is connected to the succeeding radio frequency amplifier stage 2 through coupling transformer 22. stage 2 of radio frequency amplification connects to the radio frequency amplifier stage 3 through coupling transformer .23. The radio frequency amplifier stage 3 connects to the input of the radio frequency amplifier stage 4 through coupling transformer 24. The output of the radio frequency amplifier stage 4 couples to the input circuit of the detector tube 5 through the coupling transformer 25. The output circuit of detector tube 5 connects to the audio frequency amplifier stage 6 through separate paths each having a different frequency characteristic. The separate paths have been indicated by transformers 26 and 21. The output circuit of the audio frequency amplifier stage 6 couples to the input circuit of the push-pull amplifier system 1-8 through audio frequency transformer 28. The power circuits for the several electron tubes are energized from the alternating current line circuit tapped by means of connection plug 12. The power transformer M has its primary winding adapted to be connected to the power line connection at l2 and is provided with a multiplicity of secondary windingsshown at l5, 5, I1 and 18 for supplying various parts of the rectifier circuit and the circuits of the electron tubes constituting the receiving system. The rectifier circuit includes rectifier tube l9 connected to filter circuit 20 from which connections lead to the several plate circuits of the receiving system and to the filter circuit of the sound reproducer 30.

The tone control circuit of my invention is arranged between the output circuit of the detector tube 5 and the input circuit of the audio frequency amplifier stage 6. The transformers 26 and 21 and their primary windings 3| and 32 are disposed in series in the plate circuit of the detector tube and in series with, the radio frequency choke coil 33, the lower end of primary winding 32 connecting to the resistance 34 which is arranged in the filter circuit 20. The transformer 26 is. wound in such manner that the higher audio frequencies are transferred from primary winding 3| to secondary winding 35.

The second The transformer 21 has a totally different characteristic, being arranged to transfer the low frequencies. Transformer 26 has a one-to-one ratio, while the transformer 21 has a large stepup ratio, being one-to-seven. The step-up ratio characteristic of transformer 21 has been indicated by the difference in the number of turns of primary winding 32 with respect to secondary winding 36. The primary winding 32 is shunted by a fixed condenser 31 operating to impart a peak characteristic to the transformer at low frequencies. This is fundamentally not a resonance peak as resonance and energy storage tend to increase the hangover and destroy the sharpness of the sound. The condenser 3'! acts as a cut-off for high frequencies and is of a value compared to the resistance and inductance of the primary winding 32 as'will impart the desired characteristic to the transformer. The secondary winding 36 is shunted by means of a condenser 38 which serves as a by-pass condenser to allow the secondary voltage from transformer 26 to act across the grid cathode capacity of the tube 6 instead of being dissipated in the high impedance of the transformer 21. In order to provide for the integration of the characteristic effects of transformers 26 and 21, I provide an impedance circuit disposed between a tap 39 in secondary winding 36 and the upper end 40 of primary winding 3|. This impedance circuit includes the condenser 4| and the potentiometer 42. A variable tap 43 is provided on the potentiometer which tap connects to the grounded portions of the system and effectively with the lower end 44 of secondary winding 36. The tap 43 is shiftable along the potentiometer 42 in such manner that the energy transfer paths from the output circuit of the detector tube 5 to the input circuit of the amplifier stage 6, become variably and differentially effective. As the tap 43 is moved toward the end 45 of potentiometer 42 the lower portion of the secondary winding 36, that is the turns extending between the tap 39 and the end 44 are short-circuited with a resulting decrease in primary impedance and loss of low frequency. Transformer 2! is the bass transformer. Therefore the bass is decreased by movement of tap 43 toward the end 45 of the potentiometer 42. As the tap 43 is moved toward the end 46 of potentiometer 42'the bass transformer 21 becomes more operative due to the increasing resistance across the secondary tap to ground. When this resistance is 50,000 ohms or greater, no further change in base is apparent. However, due to the .02 microfarad condenser connected between end 46 and the plate side of the audio system, the high frequencies, 3000 cycles and up, are reduced as the ground arm or tap 43 is moved toward the end 46. The combination is particularly effective, both psychologically and practically. Intermediate positions of the tap 43 on potentiometer 42 render the energy transfer paths differentially effective.

In Fig. 4, I have shown a modified arrangement of tone control circuit in which the energy transfer path for the bass frequencies extends through transformer or reactance 41 which is shunted by the .02 microfarad condenser indicated at 48. I provide a 10,000 ohm resistance indicated at 49 and serving as a coupling between the tube circuits for transmitting the high audio frequencies. The tone control potentiometer 42 in the arrangement illustratedv in Fig; 4 has a value of 50,000 ohms. The tap 43, which is shiftable along potentiometer when moved to position 46 short-circuits the lower portion of the transformer or reactance 41 and decreases the bass frequencies which may be transferred. When the tap 42 is shifted to the position $5 the bass transformer or reactance ill is wholly active thus bringing up the bass frequencies. The cone denser 4| has a capacity of .01 microfarad and when connected as shown tends to reduce the high frequencies by by-passing the 10,000 ohm resistance 49 and still further increase th apparent bass and reduce static noise.

Fig. 5 illustrates another modified arrangement of tone control circuit arranged according to my invention where all of the tone control is accomplished on the grid side of the coupling condenser 12 thus eliminating noisy operation. The 10,000 ohm coupling resistor 69 is omitted and the portion of the tone control potentiometer 42 between the tap 43 and the end &5 which connects to ground, is used in lieu thereof. With the tap 43 set on the end 05, there is no: auxiliary coupling resistance and the circuit amplifying characteristic is substantially that of the inductance capacity combination afforded by the reactance 41 and the condenser $8. This arrangement may provide exaggerated bass frequencies and a loss of high frequencies above 1000 cycles. I have found the tone control arrangement illustrated in Fig. 5 quite effective, though a shift of the tap 13 also produces an apparent change in volume.

In Fig. 6, I have shown a further modified form of tone control circuit somewhat similar to the multiple transformer arrangement illustrated in Fig. 1 except that the condenser M of .02 microfarad is shown connected between the end 45 of potentiometer t2 and the grid of the elec tron tube 6. The potentiometer in this arrangement changes the effective resistance of the primary winding 32 and correspondingly controls the amount of bass energy which is transferred from the output circuit of tube 5 to the input circuit of tube 0.

Fig. 7 illustrates an inexpensive form of tone control circuit requiring a minimum number of parts. An ideal tone control is secured using only inexpensive parts. The tone control potentiometer 42 also serves as a coupling element between the output circuit of detector tube 5 and the input circuit of amplifier tube 6. With the tone control tap 43 set at the end it of potentiometer 42, the condenser 50 forms a series reactance having high values at low frequencies and decreasing the low frequency response. When the tap 43 is set on the end 36 of potentiometer 12 condenser 50 forms a shunt reactance having high values at low frequencies thereby raising the effective bass response. The apparent volume is maintained approximately constant by the action of the coupling resistance 5!, which in the arrangement shown in Fig. 7, has a value of 5000 ohms. If the condenser 50 in Fig. 7 is replaced by a selected inductance which is opposite in impedance characteristics to the condenser 50, the connections to the ends 45 and 46 as shown must be reversed although the principle of operation remains the same. As the inductance is shifted, so far as the tone arm pick-up is conearned from a series reactance to a shunt reactance, the bass response decreases. The auxiliary decreasing of high frequencies may be accomplished in a circuit arrangement similar to Fig. 7 by using a special type of potentiometer in lieu of potentiometer 42 having 4 terminals thereby providing a double unit.

Fig, 8 shows a form of tone control circuit in which two separate controls are provided at 43 and 53 whereby the tone becomes-conformable to every operating requirement. In this arrangement the potentiometer 42 is connected in the same manner illustrated in Fig. 7 except that the adjustable tap 33 connects to the end 5 3 of the second potentiometer 55, the opposite end of which is shown at 56 connected through condenser 5? to ground. Both controls 43 and 53 are independently adjustable for effecting the required tone control.

The circuits heretofore shown are adapted to heater type tubes but may be used with the screen grid type, or with the simple filament three electrode tubes such as illustrated in Fig. 9. In this arrangement the three electrode tube 58 is coupled to the three electrode tube 50 through the transformer 60 and an intermediate circuit constitutedby transformer (ii, electron tube amplifier E32 and transformer 03. Transformer 60 constitutes the 1 to 1 ratio high frequency transformer while transformers 0i and '53 constitute low frequency bass transformers. In order to accentuate the bass, I provide the auxiliary amplifier 02 by which the bass response can be made ten to twenty times the average and thus give'an extreme of correction forany volume level. In the bass coupling system the transformer 0! has its primary winding ti l shunted by means of a .25 microfarad condenser 05. The transformer 03 has its secondary winding 00 shunted by means of the .00025 microfarad condenser shown at 08. By varying the potentiometer t0 the bass response may be selected to meet'the requirements of the particular selection being reproduced.

Fig. 2 explains more fully the theory involved in the tone control system of my invention. In this arrangement the transformers Z0 and 2? are connected substantially as shown in Figs. 1 and i. The effective resistance of the primary winding 32 of the bass transformer 2i is represented at '80. This may be the resistance of the primary winding 32 or it may be an added resistance in series with the winding 33 for decreasing the resonance effect of the bass frequency transformer. In this arrangement the potentiometer M has been shown shunted between the opposite ends of the primary windings 3i and 02 through condenser it. The movable tap 03 connects to a point H intermediate the primary windings 3i and 32. potentiometer 02 the required response curve is obtained by rendering the transformers 25 and 27 selectively effective.

In Fig. 3, I have shown a response curve obtainable in the coupling system of'my invention. The ordinates denote the amplification of the reproduced sound while the abscissa designates the frequency. The lower frequency correction is shown by the vertical line AA at approximately cycles. The transformers 25 and 27 are'connected in phase for the integrationof control currents so that with the adjustable tap 13 set at the end 06 of potentiometer 02 full operation of transformer 21 is allowed giving the resultant response curve as indicated at a. in Fig. 3. When the variable resistance is short-circuited with the adjustable tap 43 set on the end it; of the potentiometer d2, transformer 20 alone is available to establish an energy transfer path from tube 5 to tube 0 giving a response curve ideal for volume above normal as represented by curve T26. Intermediate positions of tap 03 on potentiometer 42 gives some amplification of trans- By shifting the position of tap 13 alongformer 21 and. a variation of the response curve having values shown by curves b, c and d. The ratio of the intercepts on A-A of the curves a and T26 shows the amplification ratio'this network will correct. In this case a complete tone correction for a fifteen to one amplitude variation is possible. Curve T21 shows the characteristics of transformer 21.

In the system of my invention the bass response is varied in relation to that at other frequencies. The low audio frequencies are independently controlled with respect to the other frequencies. Control may be so arranged that as the volume is decreased, the percentage of bass response increases, and as the volume is increased, the percentage of bass response decreases. The characteristics of the coupling networks have definite relation to each other, being determined from the characteristics of the threshold of audibility curve so that the amplitude above the threshold value of all frequencies shall be in a constant ratio regardless of the initial amplitude chosen for any reference frequency. Because of the fact that the average amplitude of the high frequencies is greater than the minimum bass and less than the maximum bass, a correction in quality of reproduction is obtained both above and at less than normal value. The tone control resistances in the coupling circuits may be made with such a taper that an 8 type curve is secured instead of a straight line resistance rotation ratio.

I have found the tone control system of my invention highly efficient in its operation and practical in its construction. While I have described preferred embodiments of my invention, I desire that it be understood that modifications may be made and that no limitations upon my invention are intended other than are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

1. A tone control system for amplification circuits comprising in combination an audio frequency electron tube amplifier circuit including a multiplicity of electron tubes each having input and output circuits, means coupling the output circuit of one electron tube with the input circuit of a succeeding electron tube comprising a plurality of transformers of different frequency characteristics each having primary and secondary windings, with the primary windings thereof disposed in series with the output circuit of one electron tube and the secondary windings thereof disposed in series with the input circuit of the succeeding electron tube, and means for variably controlling the transfer of energy to said independenttransformers comprising ,a circuit including an impedance connected in shunt with the primary winding of one of said transformers.

one point on said impedance being connected to a point intermediate said series connected primary windings.

2. A tone control system for audio frequency amplification circuits comprising in combination a plurality of electron tubes each having input and output circuits, means coupling the output circuit of one electron tube With the input circuit of a succeeding electron tube comprising a multiplicity of transformers of different frequency characteristics each having primary and secondary windings, the primary windings of said transformers being connected in series with the output circuit of said first mentioned electron tube and the secondary windings of said transformers being connected in series with the input circuit:

of said second mentioned electron tube and means 7 comprising a resistance connected with one end of one of said primary windings and an adjustable tap on said resistance connected to the other end of said last mentioned primary winding for differentially controlling the passage of energy through that portion of the circuit shunted by said resistance.

3. A tone control system for audio frequency amplification circuits comprising in combination a plurality of electron tubes each having input and output circuits, means coupling the output circuit of one electron tube with the input circuit of a succeeding electron tube comprising a multiplicity of series connected paths disposed in the output circuit of one electron tube and interlinked with the input circuit of the succeeding electron tube, said paths being selective to different bands of audio frequencies, means connected in shunt with one of said multiplicity of series connected paths, and including a control element for variably controlling the transfer of energy through said paths, and a capacity connection between one end of said means and the grid of the succeeding electron tube.

4. A tone control system for audio frequency amplification circuits comprising in combination a plurality of electron tubes each having input and output circuits, means coupling the output circuit of one electron tube with the input circuit of a succeeding electron tube comprising a multiplicity of independent inductively coupled paths selective to different bands of audio frequencies, a control element for differentially diverting energy through any one of said multiplicity of paths in varying, proportions for controlling the character of the energy in the output circuit of said amplification circuit and a capacity connection between one side of said control element and the grid of the succeeding electron tube.

5. A tone control system for audio frequency amplification circuits comprising in combination a plurality of electron tubes each having input and output circuits, means coupling the output circuit of one electron tube with the input circuit of a succeeding electron tube comprising a multiplicity of independent paths connected in series, each being selective to different bands of audio frequencies, and an impedance connected across one of said paths, a control element for differentially controlling the amount of energy transferred through each of said paths for controlling the character of the energy in the output circuit of said amplification circuit and a capacity connection between one side of said impedance and the control grid of said electron tube.

6. A tone control system for audio frequency amplification circuits comprising in combination a plurality of electron tubes each having input and output circuits, means coupling the output circuit of one electron tube with the input circuit of a succeeding electron tube comprising a multiplicity of independent paths connected in series and selective to different bands of audio frequencies, an impedance connected in shunt with one of said paths, and means for differentially controlling the proportions of the energy diverted to either of said paths for controlling the character of the energy in the output circuit of the amplification circuit.

7. In an audio frequency amplification system, a tone control circuit, means connected with said tone control circuit for transferring energy from one amplification stage to a succeeding amplification stage, said means including a pair of transformer circuits in series for transferring energy having an average amplitude of high frequency energy greater than minimum bass and less than maximum bass, and means for correcting the characteristics of the transformer circuits both above and at less than normal value of the energy transferred comprising an adjustable impedance connected in shunt with one of said transformer circuits.

8. In an audio frequency amplification system, a multiplicity of electron tube stages, a pair of transformers having their primary windings disposed in series with the output circuit of one electron tube stage and their secondary windings disposed in series in the input circuit of the succeeding electron tube stage and constituting coupling circuits for establishing a plurality of paths between the output of one amplification stage and the input of a succeeding amplification stage, an impedance circuit in one of said coupling circuits for selectively controlling the amplitude of energy transferred from one amplification stage to the succeeding amplification stage at predetermined amplitude and frequency, and control means operating upon one of said plurality of paths for selectively determining the amount of energy transferred through each of said paths.

9. A tone control circuit for signal receiving systems comprising a multiple stage amplifier, each stage including an electron tube having grid, cathode and plate electrodes, input and output circuits interconnecting said electrodes, a pair of transformers operative over different audio frequency ranges and each having primary and secondary windings, the output circuit of one of said amplifier stages including the plate electrode of the electron tube in said stage, the primary windings of each of said transformers connected in series, a source of potential and the cathode of the said electron tube, the input circuit of the succeeding amplifier stage including the grid electrode, each of the secondary windings of said transformer in series, and the oathode of the electron tube in the said stage, a condenser connected in shunt with the secondary winding of one of said transformers, and an adjustable resistance connected in shunt with the primary winding of said last mentioned transformer and operative to control the relative amounts of energy transferred from one amplifier stage to the succeeding amplifier stage over the respective frequency ranges of the said transformers.

10. A tone control circuit for signal receiving systems comprising a multiple stage amplifier, each stage including an electron tube having grid, cathode and plate electrodes, input and output circuits interconnecting said electrodes, a pair of transformers operative over different audio frequency ranges and each having primary and secondary windings, the output circuit of one of said amplifier stages including the plate electrode of the electron tube in said stage, the

primary windings of each of said transformers connected in series, and a source of potential and the cathode of the said electron tube, the input circuit of the succeeding amplifier stage including the grid electrode, each of the secondary windings of said transformer in series, and the cathode of the electron tube in the said stage, an adjustable resistance connected in shunt with the primary winding of the said transformer which is operative over the lower range of audio frequency energy and a condenser connecting one end of said resistance with the grid electrode of the succeeding electron tube for controlling the amount of higher audio frequency energy which is transferred from one amplifier stage to the succeeding amplifier stage.

11. A tone control circuit for signal receiving systems comprising a multiple stage amplifier, each stage including an electron tube having grid, cathode and plate electrodes, input and output circuits interconnecting said electrodes, a pair of transformers operative over different audio frequency ranges and each having primary and secondary windings, the output circuit of one of said amplifier stages including the plate electrode of the electron tube in said stage, the primary windings of each of said transformers connected in series, with a source of potential and the cathode of the said electron tube, the input circuit of the succeeding amplifier stage including the grid electrode, each of the secondary windings of said transformer in series, and the cathode of the electron tube in the said stage, an adjustable resistance connected in shunt with the primary winding of the said transformer which is operative over the lower range of audio frequency energy and a coupling device connected between one end of the resistance and the grid electrode of the succeeding electron tube for controlling the amount of higher audio frequency energy which is transferred from one amplifier stage to the succeeding amplifier stage.

' 12. A tone control system for audio frequency amplification comprising the combination of a plurality of vacuum tubes each having input and output circuits, means coupling the output circuit of one tube with the input circuit of a succeeding tube comprising a multiplicity of transformers of different frequency characteristics, the primary windings being connected in series with the plate of said first mentioned tube and the secondary windings being connected in series with the input circuit of said second tube, a condenser shunted across one of said primary windings, a circuit conductive to direct current shunted across said condenser and adjustable means for regulating the current flow through said last named circuit whereby the plate voltage of said first tube is controlled.

KENNETH W. JARVIS. 

